Plasma disappearance curves of radiolabeled bilirubin, sulfobromophthalein, indocyanine green and bile acids are obtained in normal volunteers and in patients with hepatic disease. Curves are analyzed by computer to calculate anion clearance (e.g., CBR, (ml/min/kg); CBSP, etc.), and, in the case of bilirubin, daily bilirubin turnover (BRT (micron mol/kg/day). Data are further analyzed in terms of compartmental models to estimate hepatic uptake and conjugation rates, storage capacity, liver:plasma concentration gradients and other parameters of physiologic interest. These studies permit precise in vivo quantification of individual steps in the hepatic organic anion transport mechanism in man, which are useful both for physiologic studies and in the diagnostic classification of hepatic dysfunction. Micromodifications of the above techniques have been developed which permit analogous data to be obtained in small animal models such as the rat. In addition to these in vivo physiologic studies, a technique has been developed for the isolation, purification, and radiolabeling of conjugates of bilirubin. It is expected that the availability of these purified preparations of bilirubin conjugates will, for the first time, permit detailed studies of both the hepatic and renal excretion of conjugated bilirubin.